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2012 Pro-4X Sudden 3MPG drop!?

5K views 31 replies 8 participants last post by  HFD1 Tuner 
#1 ·
Howdy all,

I've got a problem here that is driving me nuts and I hope you can help. First, let me note that I've searched the forums but not found an answer to my satisfaction, so I apologize in advance for another MPG related thread.

My wife and I bought a brand new Pro-4X with 200 miles on it on Sept. 1, 2012 as I wanted one of the last Nashville produced models before they moved production to Georgia (funnily enough, I also just moved to Nashville from Delware in January). I immediately installed a flat KN drop in filter and swapped the factory tires for Cooper ST MAXXs of the same size. These are my only mods as of yet.

Once we got it over the break in period (i.e., 2000 miles), I was hitting 16.5 in town, and 19.8(!) on the interstate at 70 mph with cruise on. I was a super happy camper.

We hit about 4,000 miles on the odometer around Halloween 2012, which was also when the temperature in Delaware dropped to cold as heck, and, I assumed, the winter gas blends kicked in. I also got my first oil change then.

In early November 2012, when I started using the heater for the first time, I noticed the sound of "drops" hitting the factory skid plate. The car had never had ANY leak of any kind before (that I could hear). I figured this was due to the compressor being on and generating some condensation. Regardless, the truck still emits some of these drops now, whether or not the heater is or has been on. I have looked underneath, and none of the drops appear to be anything other than water.

Also in early November 2012, I noticed a terrible drop in gas mileage. I went down to 16.5 on the interstate (70 mph with cruise on) and about 12.2 in town. I have not changed my driving habits, am not a lead foot, and generally am cognizant of my RPMs. In sum, I'm the guy who pays careful attention to my enginge performance and driving style.

Last, although I'm not sure because I've never owned an Xterra before, I think the truck started shifting too much/easily at city speeds (e.g., from start to about 40 mph) at some point close to the mileage drop. Compared to the 1996 Explorer I was previosuly driving, the Xterra seems to shift up and down WAY TOO MUCH on relatively flat city roads, especially around 30-40 mph.

Has anyone else experienced this weird drop in MPGs? I had read a lot of positive reviews on modern Xterra fuel efficiency, but am baffled and concerned by this development. I thought it could be winter gas, cold weather, underinflated tires (I'm always at 50 psi on the MaXXs), but surely none of these is the reason for my loss of 3MPG!

I know these trucks are gas guzzlers compared to hybrids, and I'm ok with that. However, the sudden loss of 3MPG for no reason worries me, and is too much of a drop for me to just let it go.

Besides, I want to get a Shrockworks front and rear bumper installed. These 3 MPGs were the ones I was saving to sacrifice to the Shrock!

Any and all suggestions are welcome!!

Thanks!

Son of a Gunsmith
 
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#2 ·
That is concerning... hmmm...

3MPG loss at 4000 miles, and a strange drip hitting the skid that appears to just be water even though you're not running the AC.

My first concern with that drip is the radiator which is right there. I'd be worried that there might be a problem with a hose and that it's loosing water slowly. But being as new as it is I'm sure it'd be filled with coolant and not water, so condensation is more likely, but the heater shouldn't create condensation and you're definitely not running the AC at this time of year... chances are it's completely unrelated to the MPG drop though if you're not seeing anything over heating.

Winter gas can definitely hit fuel economy hard, and you also say you just moved... to Nashville from Delaware... Delaware is much closer to sea level than Nashville but I wouldn't imagine it'd be a terrible change... 60ft vs 500ft, nope that shouldn't be too significant.

OK a couple of variables to get out of the way:

First, what kind of oil was changed into the Xterra, was it a good brand and was it the proper weight.

Second, what kind of fuel is it getting? Did you start using a different brand, different grade?

Third, have you checked the airfilter and made sure nothing's clogging it up? If an engine can't breathe it'll use more gas for sure.

Fourth... I haven't quite come up with a fourth yet but I'm working on it...

The transmission issue with the constant shifting would seem to indicate that the X is working harder than it should be to put down the same force (or at least thinks it needs to work harder). This can be caused by weight or friction... bad oil or the wrong weighted oil can do that inside the engine, the ebrake stuck in the engaged position can add that kind of friction too.

OK once we have that we can move from there.
 
#4 ·
Thanks REVU. Here are the answers to your questions, going backwards:

Fourth. The KN is an oiled filter. But I noticed the drop some thousand or more miles after putting it in.

Third. amazingly, the air filter is completely clean. Visually the KN looks like it did out of the box. Clean it anyway? Still nice and oily.

Second. I have generally used regular unleaded from a variety of stations in Delware and Penn. I had hoped the crappy mileage was indicative of DE's bad winter gas, but being back in NAshville hasn't seemed to affect it at all. Still crap mileage. I tried a few tanks of premium over the course of a 1000 mile trip in December, and that boosted my MPG some, but not enough to justify switching to that gas.

First. I do not know about the oil, as I took it to the local Nissan dealer in Wilmington DE. I assumed they put in the right stuff. Mistake?

Generally, the weight issue shouldnt be a problem as it is empty and I already have a baseline from the increased weight of the cooper tires since I never drove it without them. I have checked the e-brake in the past and am sure it is not on or partially engaged (based on me making sure the pull bar is down from the inside of the truck - I wouldn't know how to look underneath to see if it was still engaged).

I also am sure the tires are wearing very well as I haven't lost any measurable tread in 8000 miles. (E load tires YAY!)

Any other thoughts?

Thanks for the response!


No lights are coming on at all, and the car seems like it is running as it should.
 
#5 ·
One would imagine the dealership knows what oil to put in, but I've seen dealership techs screw stuff up before. I believe the accepted oil weight viscosity range for the VQ40 is 5w-30, 10w-30, and 10w-40. I usually use synthetic 10w-30 in my X and it's done really well with that. If it's getting really cold where you are you could try the 5w-30 that holds viscosity better under colder conditions. If the temperatures aren't too cold then you might try the 10w-40 and see if it makes any difference on the hotter end.

It sounds like your air filter is really new so it would be odd for that to be the problem then. And if it was over oiled sometimes the excess oil can get on the MAF sensor and cause weird things to happen. Normally that will trip a check engine light though. And being that you changed it after you were already experiencing issues probably removes that from the equation.

As you have been fueling at an array of different fuel marks, you might try running a fuel system cleaner through your tank - people would probably say something like seafoam or Magic Fuel, I haven't used those so you'd want to read up on them or ask around someone who has. There are also lots of generic fuel system cleaners available through autozone and such, but people around here generally say to go with particular brands that are known to work well. (And not all gas is equal, around here I've seen Circle K gas gunk up engines pretty good because of cheap chemicals and containers that they keep it in.)

The constant transmission shifting is still making me think it's a frictional issue. Somewhere it's working harder than it should be for some reason, and that can definitely cause it to run inefficiently. When it shifts does it shift fast or is there a lag between gear catches?

I'm sure there's a reason somewhere close by.

Keep at it and god luck :biggrin:
 
#6 ·
I will try a new oil change using your recommendations this weekend as its time for another now.

I have not oil the KN; I just dropped it in right out of the box, and havent reoil yet, since it looks clean. Perhaps I should try the old stock filter and see what happens. Is there a way to find the MAF sensor to see if it is gunked up? Would I even be able to tell?

I will try a fuel treatment at my next fill up and see what happens. I will report back on here after that.

As far as shifting, I think it shifts too easily. It doesnt lag or catch as if the tranny is going out (sadly, I've had that happen in my other older trucks over the years). I have been wondering if all xterras shift this easy, as it seems like it shifts into higher gears when it should just stay in the same lower gear given the speed, terrain and city driving. I wonder if I can get a power chip of some sort that will make it stop shifting so easily and stick in a gear longer...

Thanks again for the input! Will take all I can get. This truck is my baby and I plan to do some mods once I get this sorted out.
 
#7 ·
Definitely! I bet once it's sorted it'll be golden for a long time.

As far as the MAF goes it can be really hard to tell if oil has gotten on it or anything like that. There are MAF cleaners on the market, but it's almost better to stay away from those because if it's not done just right it's really easy to break the sensor and then need a completely new one. So it's risky especially when it's not throwing any code.

Switching into higher gears? That it will do, like if you're cruising at 30MPH and doing fine in 4th gear but it wants to go into 5th gear and so on. Turning off Overdrive using the little button on the gear shifter will help with that some, you just have to remember to turn it back on when entering the highway.

Do let us know what happens after the oil change and fuel treatment though.
 
#8 ·
I was thinking of the Overdrive button last night but wanted to research what that would do on the city streets before I tried it. I think I will give that a shot as well.

Planning an oil change along with fuel treatment this weekend. Will probably try a top synthetic as many have recommended on here.

Will be in touch!
 
#9 ·
Update: Since my last post, I've been drying in town with Overdrive OFF, switching it on only when I hop on an interstate. This seems to have recovered about 1-1.5 MPG and makes the truck shift less on slightly hilly roads at 30-40MPH. I also noticed with OD off that my idle goes down about 100 RPM.

Last night I did an oil change at 8800 miles, putting in the best synthetic the Jiffy Lube guys had. I also added a bottle of fuel treatment picked up from an autozone. I took out the K&N for a good wash and replaced it with the original (and still brand new/clean) paper air filter.

The K&N looked perfectly clean and well oiled just like it did out of the box, even though it hasn't been cleaned in 8000 miles. No particles I could see actually came out during the washing (which I did with the proper KN kit liquids). I have driven through some TERRIBLE salt and snow storms this winter, but could not see or feel any salt grit coming out of the filter. Its drying now and I will lightly re-oil and reinstall later today or tomorrow so as not to skew my results by altering too many variables at once.

Also, I've been paying attention to the locatio nand speed of the drip, though i can't get under to see it again yet. I hear drips hitting the skid plate closer to the middle of the truck (I'd say approximately under the driver's area rather than the engine bay). These still occur in dry conditions and whether or not I turn on any accessories like the heater or AC. The truck did not drip for the first couple thousand miles so I wonder if perhaps some hose could have come loose and I'm loosing power/something out of a bad seal that affects my MPG.

Will update again after putting this treated tank of gas through it.
 
#10 ·
Tracing down a problem can be one of the hardest things to do especially when it's not causing a major impact on the performance of the vehicle. Just that whole process of elimination thing. Glad you've got some progress there with the OD, I'm a little confused by the idle speed, but we won't worry about that.

Once it's had a chance to eat through some treated gas I'll be really curious as to how it performs. Thanks for the update :biggrin:
 
#12 ·
Thanks for the thoughts CC2, but I doubt it is a fuel leak. I can't smell gas at all.

Update: I have gone through a single tank of treated gas running with an oil change using the best synthetic Jiffy Luve had. MPG driving as normal in town now breaching 14 MPG. Dont know if this coincides with a somewhat modest increase in atmospheric temperatures or just my treatments to the truck. Planned ot do ECU reset yesterday, but that got siderailed by a work project.

I also parked the front end of the truck up on a curb so I could crawl underneath to investigate that drip I always hear. Can't locate the actual source of the drip with all the (flimsy) skid plating underneath there, but does seem to be just water as when the truck tilted a bit some of the flid poured out onto the ground. Doesnt SEEM to be coming from Engine bay; rather it seems to be coming from the exhaust or gas tank area.

Will keep posting with updates.

Also, can someone please confirm that I need a 10mm wrench to get the battery cables off? I also want to remove the mudflaps, but think I'll have a shop do that when I get them rotated this week.

Best,

Son of a Gunsmith
 
#13 ·
So helped some, hmmm...

Off the top of my head I can't confirm for sure that the battery tie downs are 10mm, but 90% of the bolts on the X are 10mm. The battery ones might be a little smaller though... like an 8mm.

The mudflaps aren't hard to take off, but I had to fit a phillips bit into a wrench because there wasn't enough room between the tire and flap to fit a screw driver. If they're rotating the tires they'd be easy to take off. Some of the screws do have to go back on though to keep the wheel well liner in place.

Definitely keep us up posted on the progress with the MPGs after the reset.
 
#14 ·
Do you drive around with the heat on front defrost. if so, your ac runs to pull the moisture out of the air and off the glass. That could explain some of the mpg drop. That combined with crappy winter gas (ethanol makes it even worse) makes me see about a 5 mpg drop in the winter on average vs when I could still find non ethanol gas in the summer. ethanol gas really just showed up around here in the last year or so and I absolutely despise it.
 
#15 ·
are we 100% sure he isnt leaking fuel? he said it appeared to be coming from fuel tank area. also check for leaking injectors, follow the fuel rail from the injectors back to the fuel lines and fuel lines back to tank and watch for leaks all the way back he may have hit something and caused a small hole in a fuel line somewhere. you dont necessarily smell fuel with every fuel leak, does the truck have a warranty? if so i would see if leaks are covered and see if they will fix it for free
 
#16 ·
If you are pretty sure the leak is water, then I think Intender might be on the mark. The a/c will definitely hit the M.P.G.s and will have water drain out of the airbox as a side effect.. To check this, run at idle with the heater on. If you hear the a/c cycling, then there's your prob.. The a/c is supposed to be active in the defrost settings, but not in any of the heater settings.
Good Luck!!
 
#17 ·
but 3mpg is alot for a/c to take my first gen v6 doesnt lose that much and i run it almost all the time(texas, so if its not so hot i need the a/c its cold and humid and needs defroster) and get 15-17mpg average and thats right on the mark on its ratings the 2012s are way more efficient then the 2000s so you would think you would hardly notice the a/c on mpg side, lucas (the clear bottle, and ethanol treatment) and seafoam are what i use to clean fuel system give em a shot, but this sounds to me like you changed something either consciously or not it may have been the location change or maybe your getting bad gas, try to stay away from ones right off freeway and off branded gas go to a reputable station and stick with it for awhile. but that much water coming off a/c if it is isnt a good thing anyway you slice it. check to see if your compressor maybe stuck on, if so that would cause it to over work as the compressor shouldnt run 100% of the time even with a/c on it should cut off occasionally
 
#18 ·
All,

Thanks for the additional comments. I will try to check the compressor. I'm 100% certain I get the leak anytime I have the heater on, but I'm also 95% certain I get the leak/drip with the heater OFF too. When I have the heater on, I usually direct the airflow to the floor or the floor and face setting. I actually don't think I've ever had it set to defrost.

I'm really hoping that its not just a combination of winter gas, cold temps, and short trips. At this point, I'd prefer to find out that I need something under warranty replaced than suffer from crap fuel efficiency well below what I anticipated without mods. who knows, maybe the ECU reset this weekend will fix it. Once I try that and exclude mechcnical problems underneath, I may have to conclude that I just get terrible mileage when I only drive 8 or less total miles to/from work each day. Only about 2 miles of that each way is 60 mph on the Nashville interstate.
 
#20 ·
, I may have to conclude that I just get terrible mileage when I only drive 8 or less total miles to/from work each day. Only about 2 miles of that each way is 60 mph on the Nashville interstate.

we have a winner. its your short trips and the shitty shitty interstate driving around here. Where does all the traffic come from anyway? there aren't that many people in this "city" to have so much congestion.

I might also venture to guess somewhere along the line you got a bad tank of gas and there is/was some water in the system. what did you use for fuel system cleaner? what concentration? You might need to run a very thick mix of something with a good demulsifier in it.

Does the 2nd gen X have a 6speed auto trans? If so the shifting could just be that it has a lot of gears.

If you are interested you can shoot me a PM and I can take a look around to check if I see anything obvious. I'm fair with general mechanical skill/knowledge. I work in cool springs, live in east nashville.
 
#21 ·
Haha - I should have said that I read a lot of positive reviews of xterra fuel efficiency compared to the older ones. Seems like 20MPG is a reasonable expectation for interstate travel in a new pro4x (unmodded).

My issue with crap MPGs started a few months ago back in Delaware however, where it is possible that I got many tanks of crap gas. I'm planning to run a bottle of techron through each tank for the next couple tanks. I also bought a bottle of seafoam to run through the engine and the tank, but need to read up on how to properly do that first. I'm no mechanic so I'll take you up on that offer when I'm free of the office one day!

(Sidenote: noticing your avatar, I will add that while I'm no car mechanic, I am a gunsmith. I grew up in my father's gunshop in Fort Smith Arkansas, and plan to start shooting compettively again now that I'm back in nashville.)
 
#22 ·
dont waste your money on the techron or seafoam. Those are basically solvents for cleaning up dirty old crap.

my hunch is excessive water in the fuel system for which you need a demulsifier.

From wikipedia...


Demulsifiers, or emulsion breakers, are a class of specialty chemicals used to separate emulsions (e.g. water in oil).

I'm getting more familiar with them now that my other vehicle is a diesel but I just gave myself a good reason to find one that works in gasoline as i left the tank lid on my bike open last night during the rain storm. (shit!) Give me a few minutes and I'll look up what should work for us.
 
#23 ·
for gasoline basically you need a good amount of methanol to act as a demulsifier.
 
#24 ·
2/25/2013 UPDATE: ECU reset FTW! Yesterday was sunny and beautiful so I took the Truck Named Sue out for an ECU reset. Unhooked the negative cable for 40 min while enjoying an excellent cigar with a buddy, then we reconnected and took it for a 60MPH drive south down I65 out of Nashville. Never broke 2000RPM and drove out 30 miles then right back doing same. All in all, I drove it 60 miles doing 60MPH and the truck computer was estimating my mileage at 22.2 MPG!

I know these things are often way off and will measure the next few tanks manually as normal, but man oh man, that was a number I've NEVER seen on the Xterra. EVen if the real mileage is ANYWHERE close to that, I'll be one happy freakin camper!

Will keep you posted over the next couple tanks to see what it does with in otwn mileage and driving at 70 MPH. If this holds through March, I'll order my Shrocks at the end of the month!

Thanks all and stay tuned!

Son of a Gunsmith.
 
#25 ·
2/25/2013 UPDATE: ECU reset FTW! Yesterday was sunny and beautiful so I took the Truck Named Sue out for an ECU reset. Unhooked the negative cable for 40 min while enjoying an excellent cigar with a buddy, then we reconnected and took it for a 60MPH drive south down I65 out of Nashville. Never broke 2000RPM and drove out 30 miles then right back doing same. All in all, I drove it 60 miles doing 60MPH and the truck computer was estimating my mileage at 22.2 MPG!

I know these things are often way off and will measure the next few tanks manually as normal, but man oh man, that was a number I've NEVER seen on the Xterra. EVen if the real mileage is ANYWHERE close to that, I'll be one happy freakin camper!
Awesome news! :thumbup: Isn't it amazing that disconnecting power fixes so much in these computer equipped cars? sometimes I wonder if all of us should have an nationwide Xterra ECU reset day every year just in case. Maybe we could do it on earth day.

If this holds through March, I'll order my Shrocks at the end of the month!
Doh! MPG :bonvoyage:
 
#26 ·
Haha. Yeah that is just amazing. I'm not sure how/why it went off the mark like that as I never disconnected the battery for more than 5 seconds since I bought it. Regardless, I'll happily watch my MPGs stay up where I though they should be for months.

I'll be totally fine losing a couple back to Shrock front and rear bumpers though. I did all that math before I bought the truck in August. This whole thread was started because I had no idea where all my MPGs went suddenly and without reason. It was like I had already installed Shrocks and was carrying another full set in the trunk!

Figure once my mileage proves itself to be ballpark of 20 with only the KN drop in filter, I'll add the bumpers, lose a couple MPG, and hopefully add exhaust and gain back some power and maybe an MPG.
 
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